1. Field of the Invention
The present invention relates to an olefin polymerization reaction unit and to a process for producing polyolefins using such an reaction unit.
2. Related Background Art
Olefin polymerization may be carried out by polymerizing an olefin monomer in the presence of a catalyst and forming granular polyolefin particles. One such process that is known to the art involves carrying out polymerization using a single-stage gas phase polymerization reactor having one polymerization stage, using a single heat exchanger to cool and partially condense unreacted monomer-containing gases recovered from the polymerization reactor, and carrying out heat removal within the single-stage gas phase polymerization reactor by again feeding the gases and condensate to the polymerization reactor (see, for example, Japanese Patent Application Laid-open No. 2000-302807).
Olefin polymerization is also carried out by a process that uses a multistage gas phase polymerization reactor which is divided into two or more polymerization stages, wherein polyolefin particles move from an initial stage to a final stage and, at the same time, an olefin monomer-containing gas is fed from the final stage toward the initial stage (see, for example, U.S. Pat. No. 5,235,009 and Japanese Patent Application Laid-open No. 2003-277412). Heat of reaction removal in such a multistage gas phase polymerization reactor is generally carried out by using a heat exchanger to lower the temperature of unreacted monomer-containing gases recovered from the initial stage of the polymerization reactor, then feeding the gases again to the final stage of the polymerization reactor.